Turbine nozzle vane mounting means



Jan. 29, 1963 J. PETERSON 3,

TURBINE NOZZLE VANE MOUNTING MEANS Filed Aug. 16, 1960 3 Sheets-Sheet l/a.

IN VEN TOR. CHARLES J. PETERSON AT T ORNE Y5 Jan. 29, 1963 c. J.PETERSON 3,075,744

TURBINE NOZZLE VANE MOUNTING MEANS Filed Aug. 16, 1960 s Sheets-Sheet?Jan..29, 1963 c. J. PETERSON 3,075,744

I TURBINE NOZZLE VANE MOUNTING MEANS Filed Aug. 16, 1960 s Sheets-Sheeta FIG: 5

3,075,744 TURBINE N OZZLE VANE MOUNTING MEANS Charles J. Peterson, NorthPaim Beach, Fla, assignor to United Aircraft Corporation, East Hartford,Conn., a corporation of Delaware Filed Aug. 16, 1960, Ser. No. 49,979 7Claims. (Cl. 253-78) This invention relates to axial flow gas turbines,and deals more particularly with improved means for mounting the nozzlevanes of such a turbine.

One object of this invention is to provide an improved mounting meansfor the nozzle vanes of an axial flow gas turbine whereby the vanes areso supported as to be capable of moving slightly in various differentdirections to compensate for thermal differentials and to thus eliminatethermal stresses acting in various different directions relative to thevanes.

Another object of this invention is to provide a nozzle vane mountingmeans which is so constructed as to simplify the installation andremoval of the individual nozzle vanes to and from the nozzle ring.

A further object of this invention is to provide an improved mountingmeans for turbine nozzle vanes which are cooled by air circulatedthrough the bodIes thereof, and wherein part of the mounting structureof each vane additionally serves as part of the means for supplyingcooling air to the vane body.

Other objects and advantages of the invention will be apparent from thedrawings and the following description.

The drawings show a preferred embodiment of the invention and suchembodiment will be described, but it will be understood that variouschanges may be made from the construction disclosed, and that thedrawings and description are not to be construed as defining or limitingthe scope of the invention, the claims forming a part of thisspecification being relied upon for that purpose.

Of the drawings:

FIG. 1 is a fragmentary front elevational view of a turbine nozzle ringembodying the vane mounting means of the present invention, with variousparts thereof being broken away to show more clearly the structure ofother parts,

FIG. 2 is a developed view of the outer periphery of the nozzle ringshown in FIG. 1, with various parts being broken away to show moreclearly the structure of other parts,

FIG. 3 is a sectional view of the nozzle ring shown in FIG. 1 with theview being taken generally along the longitudinal axis of the turbineand with parts appearing in back of the plane of the view being omittedfor clarity,

FIG. 4 is a sectional view through a nozzle vane taken on the line 4-4of FIG. 3,

FIG. 5 is a view generally similar to FIG. 3 but showing the innerretainin ring removed and the vane swung forwardly preparatory to itsremoval from the nozzle ring, and,

FIG. 6' is an exploded perspective View of the outer portion of a nozzlevane and the associated structure of the outer vane retaining member.

Referring now to the drawings, a nozzle ring embodying the presentinvention is indicated generally by the reference numeral 10 in FIGS. 1and 3. The illustrated nozzle ring is incorporated in an axial flow gasturbine and cooperates with the first stage turbine wheel, not shown.The nozzle ring 10 includes a plurality of nozzle vanes 12, 12 which arearranged in an annular series about the axis of the turbine and serve todirect motive fluid to the blades of the adjacent turbine wheel.Referring to FIG. 3, it will be'understood that the turbine wheel islocated to the right of the vane 12. High pressure motive fluid issupplied to the nozzle ring it by an annular full admission duct whichis generally a part of the outlet duct of a combustion chamber locatedupstream from the nozzle ring. In FIG. 3 such a duct is shown tocomprise an outer combustion chamber ring 14 and an inner combustionchamber ring 16, the rings being concentrically arranged about the axisof the turbine. The inner ring 16 is supported from a suitablestructure, not shown, by a support member 18.

The annular series of vanes 12, 12., as shown in FIG. 1, are of agenerally uniform shape and of equal radial length, and are arranged sothat their inner and outer ends are located respectively alongconcentrically arranged circles. The vanes are supported at both theirinner and outer ends by inner and outer annular supporting structureswhich extend along and adjacent to thevane ends.

The supporting structure or mounting means associated with the innerends of the vanes 12, 12 is such that these ends are held in fixedpositions so as to be relatively immovable with respect to each otherand with respect to other fixed parts of the turbine. As shown in FIGS.1 and 2, this supporting structure preferably includes an annularsupport member 20 which in the present case comprises a part of theinner rear case of the combustion chamber and is rigidly supported withrespect to the outer case of the turbine by suitable means. At itsdownstream end the annular member 20 is provided with a radiallyoutwardly extending flange 22 having an annular upstream directed lip 24formed along its outer margin. The annular support member 20 alsoincludes another radially outwardly extending flange 26, spaced upstreamfrom the flange 22, to which is connected the radially inwardlyextending flange 28 of an annular retaining member 30. The two flanges28 and 26 are held in connected relationship by a plurality of bolts,such as that shown at 32, and the retaining ring 30 is slidable axiallyupstream with respect to the member 20 for removal therefrom when thebolts 32, 32 are removed.

At its inner end each of the vanes 12, 12 is provided with an innershroud 34 which extends generally circumferentially of the vane. Theinner shrouds 34, 34 are so dimensioned and arranged that when all ofthe vanes 12, 12 are properly positioned in the nozzle ring 10 eachshroud 34 will abut the shroud located to either side thereof so thatall of the shrouds will collectively define a substantially closedshroud ring which confines the flow of motive fluid therethrough to anaxial direction and prevents the same from flowing radially inwardly andout of its intended path. Along its trailing edge each of the innershrouds 34 is radially enlarged and provided with a downstream facingrecess 36 dimensioned to interfit with the annular lip 24 formed on theflange 22. This interfitting relationship between the recess 36 and thelip 24 prevents the vane 12 from moving radially with respect to thesupporting member.

In addition, each vane 12, as shown best in FIG. 1, is also providedadjacent the trailing portion of its inner end with a radially inwardlyextending notch 38 which provides two radially extending andcircumferentially spaced surfaces 40, 40 facing in opposite directions.In.- terfitted with the notch 38 is a radially outwardly extending lug42 formed on the retaining member 30. The lug 42 provides two radiallyextending circumferentially spaced surfaces 44, 44 which are engageablewith the notch surfaces 40, 40 and cooperate therewith to preventcircumferential displacement of the vane 12 with respect to theretaining member 30 and the supporting member 20. Preferably, each vaneis additionally circumferentially restrained adjacent the leadingportion of its inner end and for this purpose each vane is provided onits inner Patented Jan. 29, 1963 end with a radially inwardly extendinglug 46 which interfits with a corresponding notch 48 provided in theretaining member 30. The lug 46 and the notch 48 each providecooperating radially extending and circumferentially spaced surfaceswhich coengage and restrain the vane against circumferential movement.The inner ends of the vanes are axially held in place by an outwardlyextending annular flange 50 formed on the retaining member 30. Theflange Si), as shown in FIG. 3, has a downstream facing surface 52 whichengages the upstream end surfaces 53, 53 of the inner shouds 34, 34.

At their outer ends the vanes 12, 12 and the nozzle ring are supportedby means which permits both radial sliding and swivelling movements ofthe vanes. Referring to FIGS. 1 and 3, each of the vanes 12, 12 isprovided with an outer shroud 54 which, similarly to the inner shrouds34, 34, and as shown best in FIG. 2, extends circumferentially of theassociated vane 12 and abuts the shrouds 54, 54 to either side thereofso that all of the shrouds 54, 54 collectively define a substantiallyclosed shroud ring surrounding the outer ends of the vanes. Connectedwith each of the outer shrouds 54, 54 is a radially outwardly extendingstem 56 which is in turn slidably received by a ball and socket bearingindicated generally at 58. The bearings 58, 58 are carried by an annularretaining member 60 which comprises a part of the outer annularsupporting structure for the vanes and which is preferably formedintegral with the turbine case 62, as shown.

Each of the bearings 58, 58 comprises an outer race or socket member 64which fits into a corresponding opening formed through the retainingmember 60, as shown in FIGS. 1 and 3. On its inner end each socketmember 64 is provided with a peripheral flange 66 which abuts the innersurface of the retaining member 60, and the socket members 64, 64 areheld in place in the retaining member 60 by an annular seal ring 68having a plurality of fingers 70, 70 which respectively engage thebearing flanges 66, 66, as shown in FIGS. 3 and 6. The seal ring issecured to the retaining member 60 by a number of rivets 72, 72extending through the seal ring and the retaining member. The socketmember 64 of each hearing is provided with a spherical bore 74 whichreceives a ball member 76 having a corresponding spherical surface 78.The ball member 76 is retained in the socket member.

by engagement with the spherical bore and is supported thereby forswivelling movement relativeto the socket and the retaining member 60.That is, the ball member is free to rotate about a radial axis passingthrough the socket member 64 and is also free to pivot in any directionabout a pivot point located centrally of the ball member. The ballmember of each bearing is provided with an opening for s-lidablyreceiving the associated vane stem, and preferably both the opening andthe stem are cylindrical and of circular cross section so that the stemmay slide both axially and angularly with respect to the ball member.This is not essential to the invention, however, and the stems and theball member openings could be made with noncircular cross sections ifdesired.

In addition to serving as a support for the bearings 58, 58, theretaining member 60 is also preferably provided adjacent its upstreamedge with an annular recess 80 which serves to receive and hold in placea part of an annular ring .81 which is connected to, and serves as asupport and seal for, the outer combustion chamber ring 14, as shown inFIG. 3. The retaining member 60 also includes a radially inwardlyextending annular flange 82 and the seal ring 68 is so bent and shapedas to engage the flange 82 and the downstream edges of the outer shrouds54, 54 for sealing purposes, as shown in FIG. 3.

From FIGS. 1 and 3 it will be apparent that the stems 56, 56 and theball and socket bearings 58, 58 function to, support the outer ends ofthe vanes 12, 12 in such a manner that the latter ends are free to movein various directions to compensate for thermal diiferentials existingbetween the various parts of the nozzle ring and various parts of thevanes themselves. For example, the sliding engagement between the stems56, 56 and the ball members 76, 76 of the bearings permits the outerends of the vanes to expand or contract in a generally radial direction.This sliding engagement, and in addition the sliding engagement betweenthe ball members 76, 76 and the socket members 64, 64, also permits theouter ends of the vanes to twist relative to the fixed inner endsthereof so as to eliminate thermal torsional stresses which may occur inthe vanes. Furthermore, the swivably movable ball members 76, 76 permitthe stems 56, 56 to move pivotally in any direction relative to thecenters of the ball members and thereby eliminate thermal stresses whichtend to produce such pivotal movements. Thus, the support provided forthe outer ends of the vanes gives the vanes a high degree of flexibilitywhich is advantageously employed for the elimination of stresses in thenozzle ring assembly. More particularly, any tendency of a vane to twistabout its longitudinal axis, causing one end of the vane to moveangularly relative to the other, is accommodated by rotation of the vanestem 56 relative to the associated ball member 76 or by rotation of theball member relative to the associated socket member 64. Any lengtheningor shortening of the vane is accommodated by a sliding motion of thestem relative to the ball mem her. And, any tendency of the outer shroud54 to cock or move angularly from the position shown, as by a bowing ofthe vane in any direction or by different parts of the vane changing inlength by different degrees, is accommodated by rotation of the ballmember relative to the socket member about an axis generally normal tothe axis of the stem. The engagement of the shroud 54- with adjacentshrouds and with the seal ring 68 may impose some forces on the shroudtending to resist some of these motions, depending on the size anddirections of the deformations involved. Nevertheless, the shrouds arenot force fitted in relation to neighboring shrouds and the seal ring,and therefore some degree of motion of the shroud in the various mannersdescribed is possible before the reaction forces imposed thereon by theneighboring shrouds and sealing ring become very great. The illustratedball and socket joint thus provides a degree of flexibility which islacking in a completely rigid connection.

The vanes 12, 12 shown in the drawings are of a type which are aircooled. As far as certain of the broader aspects of the invention areconcerned, thevanes need not necessarily be air cooled, but when theyare so cooled one of the important features of the invention is that thevane mounting means hereinbefore described functions in a novel mannerto provide part of a system for circulating the cooling air through thevanes 12, 12. In accordance with this feature of the invention, theillustrated vanes are of a hollow construction, as shown in FIGS. 3 and4, and the stems 56, 56 are also provided with hollow bores, such asshown at 83 in FIG. 3, which communicate with the hollow interiors ofthe vanes to supply cooling air thereto. Various difierent constructionsof hollow vanes may be used with this invention, however, for purposesof illustration the vane 12 shown in FIGS. 3 and 4 includes a' hollowbody 84 which has a series of longitudinally extending grooves 86, 86formed in its inner surface, the grooves 86, 86 being separated bylongitudinally extend ing ribs 88, 88. Positioned within the hollowinterior of the vane body is a battle member '90 which engages the ribs88, 88 and closes the grooves 86, 86 so as to define longitudinalpassageways for directing the flow of cooling air along the innersurface of the vane body. The bafiie member 90 is closed at its upperend by a cover plate 92 and at its outer end is provided with aplurality of openings, such as shown at 93, which openings providecommunication between the bore 83 of the associated stem 56 and thepassageways provided by the longitudinal grooves 86, 86. Thus, the airintroduced to the vane through the bore 83 of its stem is directed tothe various 5. passageways provided by the grooves 86, 86. The innershroud 34 of each is provided with an opening 94 through which the airpassing through the vane body is discharged, the opening 94 being incommunication with all of the passageways defined by the grooves 86, 86.After leaving the openings 94, 94 of the vanes 12, 12, the cooling airenters a chamber 96 defined by the retaining member 39 and the innershrouds 34, 34, and then flows through one or more openings such as thatshown at 98 in the retaining member 30, and through one or moreopenings, such as that shown at 1% in the annular member 20, toward theaxis of the turbine from which location it is exhausted by othersuitable means, not shown.

As shown best in FIG. 3, the turbine case 62 surrounds the retainingmember 60 and, together with the retaining member, the ring 81 and theouter combustion chamber ring 14, defines a manifold 1%2 whichcommunicates with the outer ends of all of the stems 56, 56 so as tosimultaneously supply cooling air to the stems. Cooling air underpressure is supplied to the manifold 102 by any suitable means and maycomprise air which is diverted rom a compressor stage located upstreamof the combustion chamber and bypassed around the combustion chamber. Inregard to the cooling of the vanes 12, 12 it will be observed that thestems 56, 56 in this invention serve the double purposes of bothproviding for the introduction of air to the vanes and also of providinga support for the outer ends thereof.

Another feature of the present invention is that the mounting meansprovided for the vanes 12, 12 is also of a construction whereby thevanes are easily installed and removed to and from the nozzle ring. Asmentioned previously, the inner retaining member 30, which forms a partof the mounting means or supporting structure for the inner ends of thevanes 12, 12, is removably connected to the annular member 20 by thebolts 32, 32. When the member 30 is removed from connected relationshipwith the annular supporting member 20 the vanes 12, '12 are freed forpivoting movement about the centers of the ball and socket bearings 58,58. Thus, when the retaining member 31 is removed each of the vanes 12,12 may be pivoted axially upstream from the upright position shown inFIG. 3, at which the inner end thereof is located adjacent thesupporting member 20, to an inclined position, such as shown in FIG. 5,at which the inner end of the vane is spaced a substantial distance fromthe annular member 20. The spacing between the inner end of the inclinedvane and the supporting member is sufficient to permit the vane to bepulled or slid out of engagement with the ball member 76 of the bearing58 to remove the vane from the nozzle ring, as shown in FIG. 6.Likewise, when a vane is to be replaced in a nozzle ring, this operationis easily performed by first fitting the stem 56 into the opening of theassociated ball member 76 while the vane is at an inclined angle withthe axis of the turbine and by then swinging the vane to the uprightposition shown-in FIG. 3 and adjusting the same to bring the groove 36thereof into interfitted relationship with the lip 24. After all of thevanes are so positioned in place in the nozzle ring, the retainingmember 30 is replaced and reconnected with the support member 20 by thebolts 32, 32.

As used herein and in the claims which follow the term swivellingmovement refers to a movement of one part relative to another whichmovement is universal in nature in that it may occur about any axispassing through a point common to the two parts. The movement of theball in a ball and socket joint, wherein the ball may rotate relative tothe socket about any axis passing through its center, is an example ofsuch movement although other types of joints allowing the same type ofmotion are also possible. Likewise, the term swivable or swivablymovable refers to a part capable of such swivelling or universalmovement.

The invention claimed is:

1. A nozzle ring for an axial flow turbine, said' nozzle ring comprisinga plurality of generally similar and radially extending vanes arrangedin an annular-seriesv so that their inner and outer ends are disposedrespectively along inner and outer concentric circles, mounting meanslocated adjacent one of said concentric circles and serving to hold infixed and nonadjustable positions the associated ends of the saidvanes,,radially extending stems formed on the ends of the vanes definingthe other of said concentric circles, an annular retainingmember locatedalong and adjacent the latter ends of said vanes,- means independent ofsaid vanes for supporting said annular retaining member in a fixedposition relative to the axis of'said turbine and a plurality of balland socket bearings carried by said annular retaining member, each ofsaid bearings having a ball member provided with an opening whichslidably receives a respective one of said vanes stems so as to permitradial sliding movement of said vane stem relative to said retainingmember.

2. A nozzle ring for an axial flow turbine having a case, said nozzlering comprising concentrically arranged inner and outer annularsupporting structures, a' plurality of vanes arranged in an annularseries between said supporting structures, means independent of saidvanes for holding said annular supporting structures in fixed positionsrelative to said case, said vanes having their inner ends held in fixedand nonadjustable positions by connection with said inner supportingstructure, a plurality of radially outwardly extending stems formedrespectively on the outer ends of said vanes, and a plurality of balland socket bearings. carried by said outer supporting structure, each ofsaid bearings having a swivable ball member provided with an openingwhich slidably receives a respective one of said vane stems so as topermit radial sliding movement of said vane stern relative inner andouter annular supporting structures, a plurality of hollow vanesarranged in an annular series between said supporting structures, meansindependent of said vanes for holding said annular supporting structuresin fixed positions relative to said case, said vanes having their innerends held in fixed and nonadjustable positions by connection with saidinner supporting structure, a plurality of radially outwardly extendingstems formed respectively on the outer ends of said vanes which stemsare hollow andprovide conduits for the flow of cooling air to theinteriors of said vanes, a plurality of ball and socket bearings carriedby said outer supporting structure, each of said bearings having aswivable ball member provided with an opening which extends therethroughand which slidably receives a respective one of said vane stems so as topermit radial sliding movement of said vane stem relative to said outersupporting structure, and means providing a manifold adjacent the outerends of said vanestems for simultaneously supplying cooling air thereto;

4. In an axial flow-turbine having a case the combina-" between saidsupporting structures, means independent of said vanes for holding saidannular supporting structures in fixed positions relative to said case,means for fixedly and nonadjustably securing the inner ends of saidvanes to said inner supporting structure and which means includes atleast one part which is removable to permit axial movement of said innervane ends relative to said inner supporting structure duringinstallation and removal of the said vanes, said outer supportingstructure including an outer annular retaining member surrounding theouter ends of said vanes, a plurality of radially outwardly extendingstems formed respectively on the outer ends of said vanes, and aplurality of bearings carried by said outer retaining member each ofwhich bearings includes a socket member fixed to said outer retainingmember and a ball member which is swivably movable relative to the saidsocket membery'each of said ballmembers having a radially extendingopening therein which slidably receives a respective one of said vanestems so as to support the outer end of the associated vane forswivelling and radial sliding movement with respect to said outerretaining member.

5. In an axial flow turbine having a case the combination of inner andouter annular supporting structures, a plurality of nozzle vanesarranged in an annular series between said supporting structures, meansindependent of said vanes for holding said annular supporting structuresin fixed positions relative to said case, mounting means for fixedly andnonadjustably securing the inner ends of said vanes to said innersupporting structure and which mounting means includes at least one partwhich is removable to permit axial movement of said inner vane endsrelative to said inner supporting structure during installation andremoval of the vanes, said outer supporting structure including an outerannular retaining member surrounding the outer ends of said vanes, aplurality of radially outwardly extending stems formed respectively onthe outer ends of said vanes, and a plurality of stem supporting meanscarried by said outer retaining member, each of said stem supportingmeans including an apertured member for receiving a respective one ofsaid vane stems for sliding movement of the vane relative thereto alongthe longitudinal axis of the vane and means connecting said aperturedmember to said outer retaining member for pivotal movement relativethereto so as to permit the associated vane to be pivoted in a generallyaxial direction during installation and removal thereof between a normalupright position at which the inner end of the vane is located adjacentsaid inner supporting structure and an inclined position at which theinner end of the vane is spaced from said inner supporting structure,said stems being freely received in said apertured member so that saidstems may be slid into or out of said apertured members to connect ordisconnect the vanes from said outer retaining member when said vanesare in their inclined positions.

6. In an axial flow turbine having a case the combi-' nation of innerand outer annular supporting structures, a plurality of hollow nozzlevanes arranged in an annular series between said supporting structures,means independent of said vanes for holding said annular supportingstructures in fixed positions relative to said case, mounting means forfixedly and nonadjustably securing the inner ends of said vanes to saidinner supporting structure and'which mounting'means includes at leastone part which is removable to permit axial movement of said inner vaneendsrelative to saidfinner supporting structure during installation andremoval of the vanes, said outer supporting structure including an outerannular retaining member surrounding the outer ends of said vanes, apluralityof'bearings carried by said outer retaining member each ofwhich bearings includes a socket member fixed to said outer retainingmember and a; ball member which is swivably movable relative to the saidsocket member, each of said ball members having a radially extendingopening therethrough, a plurality of radially outwardly extending stemsformed respectively on the outer ends of said vanes and which stems arehollow and communicate with the hollow interiors of said vanes toprovide for the flow of cooling air to said vanes, said stems beingslidably received respectively by said openings in said ball members soas to be in communication with the space surrounding the outer side ofsaid outer retaining member and so as to support the outer ends of theassociated vane for sliding and swivelling movement with respect to saidouter retaining member, and means providing a manifold surrounding saidouter retaining member for simultaneously supplying cooling air to saidstems.

7. In an axial flow turbine the combination of inner and outer annularcase structures, an outwardly extending annular flange connected withsaid inner case structure and having an upstream facing lip locatedalong the outer margin thereof, a plurality of nozzle vanes arranged inan annular series between said inner and outer annular case structures,each of said vanes having means on its inner end defining a downstreamfacing recess adapt ed to interfit with said upstream facing lip andalso having means on its inner end defining at least two radiallyextending faces which are cirumferentially spaced and facing in oppositecircumferential directions, an inner retaining ring removably connectedwith said inner case structure and having means defining a downstreamfacing surface which engages said vanes and holds the same axially inplace with the recesses thereof in interfitted relation with said lip toprevent axial and radial movement of said vanes relative to said innercase structure, said retaining ring also having means defining aplurality of radially extending surfaces with the surfaces beingcircumferentially spaced and facing in opposite circumferentialdirections and interfitting with the two radially extending faces onsaid vanes so as to hold the associated vanes circumferentially in placerelative to said inner case structure,'an outer annular retaining memberfixedly connected with said outer case structure and surrounding theouter ends of said vanes, a plurality of radially outwardly extendingstems formed respectively on the outer ends of said vanes, and aplurality of bearings carried by said outer retaining member each ofwhich bearings includes a socket member fixed to said outer retainingmember and a ball member which is swivably movable relative to the saidsocket member, each of said ball members having a radially extendingopening References Cited in the file of this patent UNITED STATESPATENTS 2,793,832 Wheatley etal May 28, 1957 2,851,246 Nichols Sept. 9,1958 2,859,934 Halford et al. Nov. 11, 1958 2,862,654 Gardiner Dec. 2,1958 2,910,269 Haworth et al. Oct. 27, 1959 2,937,000 Ledwith May 17,1960 2,972,441 Hall Feb. 21, 1961 2,984,454 Fiori May 16, 1961

1. A NOZZLE RING FOR AN AXIAL FLOW TURBINE, SAID NOZZLE RING COMPRISING A PLURALITY OF GENERALLY SIMILAR AND RADIALLY EXTENDING VANES ARRANGED IN AN ANNULAR SERIES SO THAT THEIR INNER AND OUTER ENDS ARE DISPOSED RESPECTIVELY ALONG INNER AND OUTER CONCENTRIC CIRCLES, MOUNTING MEANS LOCATED ADJACENT ONE OF SAID CONCENTRIC CIRCLES AND SERVING TO HOLD IN FIXED AND NONADJUSTABLE POSITIONS THE ASSOCIATED ENDS OF THE SAID VANES, RADIALLY EXTENDING STEMS FORMED ON THE ENDS OF THE VANES DEFINING THE OTHER OF SAID CONCENTRIC CIRCLES, AN ANNULAR RETAINING MEMBER LOCATED ALONG AND ADJACENT THE LATTER ENDS OF SAID VANES, MEANS INDEPENDENT OF SAID VANES FOR SUPPORTING SAID ANNULAR RETAINING MEMBER IN A FIXED POSITION RELATIVE TO THE AXIS OF SAID TURBINE AND A PLURALITY OF BALL AND SOCKET BEARINGS CARRIED BY SAID ANNULAR RETAINING MEMBER, EACH OF SAID BEARINGS HAVING A BALL MEMBER PROVIDED WITH AN OPENING WHICH SLIDABLY RECEIVES A RESPECTIVE ONE OF SAID VANES STEMS SO AS TO PERMIT RADIAL SLIDING MOVEMENT OF SAID VANE STEM RELATIVE TO SAID RETAINING MEMBER. 